This article is for informational purposes only and does not replace professional medical advice.
In the Nordic countries, the incidence of melanoma has been rising at a gradual yet steady rate in the past century. Multiple smaller scale studies have previously reported an increase in age-adjusted incidence of cutaneous melanoma (CM) in the Nordic countries over the last 60 years. However, there have been few prospective population-based studies that examined the occupational variation in CM risk over a period of time. In order to understand and determine the variations in the incidence of Cutaneous melanoma, a large-scale cohort study was done beginning from 1961 to 2005 by the Nordic Occupational Cancer Study team.
The chief objective of this cohort study was to determine the occupational variation in Cutaneous Melanoma and the associated risk with various occupations.
Study Methodology
Researchers undertook a massive 45-year follow-up of a historical prospective cohort study beginning from 1961 to 2005. The information for the study was obtained by linking records between the population census and cancer registry data for Nordic residents between the ages of 30 and 64 years living in Denmark, Finland, Iceland, Norway and Sweden. The study stratified the occupations into 53 categories each of which was further designated into indoor, outdoor and mixed work to estimate sun exposure. Furthermore, the data also analyzed the socioeconomic status of the entire population to determine its role on cutaneous melanoma.
With this data, standardized incidence ratios (SIRs) were calculated for each category of occupation and socioeconomic status. The SIR was calculated by dividing the observed number of Cutaneous Melanoma cases by the expected number of cases. Data for this calculation was obtained using stratum-specific person-years and national Cutaneous Melanoma incidence rates. The higher the Standardized incidence ratio, the higher should be the risk for skin cancer in a particular occupation.
Study Findings
The study evaluated a total of 385 million person-years, among which 83 898 incident cases of Cutaneous Melanoma was found. The study found that men with outdoor work had a low SIR of 0·79 and men with indoor work had a high SIR of 1·09. The differences in women based on their occupation also found similar results as in the men with higher SIR. In the group categorized under high socioeconomic status, the risk for melanoma was found to be even higher based on their SIRs which was found to be 1.34. in men and 1.31 in women. Likewise, people who worked in military, transport, technical, and public safety workers with substantial skin exposure to carcinogens had higher risk for skin cancer.
Conclusion
The major flaw in the study was the use of SIRs to estimate skin cancer risk as the denominator in the SIR equation was based on an expected number of cases which can be substantially higher when wrongly estimated skewing the equation to the wrong end. In people with outdoor occupation, there was reportedly a higher number of cases of melanoma in comparison to indoor worker but due to the observed cases being higher than the expected cases their SIRs were calculated as low. However, the study did find that occupational and socioeconomic variation in melanoma played a significant role in terms of risk for developing this fatal condition.
References:
Alfonso JH, Martinsen JI, Weiderpass E, Pukkala E, Kjærheim K, Tryggvadottir L, Lynge E. Occupation and cutaneous melanoma: a 45-year historical cohort study of 14·9 million people in five Nordic countries. Br J Dermatol. 2020 Jul 6. doi: 10.1111/bjd.19379. Epub ahead of print. PMID: 33026672.